The present invention relates to a catheter for use within the vasculature of the human body, and, more particularly, concerns a catheter in which the stiffness, or flexibility, may be controlled during the use thereof.
Medical devices such as intravascular catheters, and the like, are placed into various body orifices for many purposes, including the infusion of fluids, withdrawal of fluid samples from the body, and for the insertion of angiography balloons. Very often, such a device has to be placed in a remote part of the body, or perhaps threaded for a considerable distance through the vascular system. Most catheters of the type designed for placement into a deep body position are made of pliable, very flexible, plastic material. Such material facilitates any bending or curving that may be necessary during placement and also serves to eliminate or decrease the traumatic effect of the insertion of the medical device. However, the relatively low flexural modulus of most catheters which provides the pliable nature of the catheter often produces difficulties in controlling the catheter as it is passed through the vascular system.
One problem which arises using most of the very flexible catheters during insertion into the vessels is the tendency of the catheter to bend and flex during the insertion stage. This action produces awkward and erratic threading of the catheter by the operator. This problem can become acute when the catheter is long and is intended to be positioned deep within the vasculature of the patient.
Catheters have employed fluid pressurization to accomplish various functions. For example, U.S. Pat. No. 3,525,329 discloses an evertable, extensible probe which when pressurized extends the probe into the body cavity to be examined. U.S. Pat. No. 3,502,069 employs a rigid tubular casing and a flexible evertable tubing inside. When fluid pressure is applied to the casing the tubing is everted out of an open end of the casing. U.S. Pat. No. 3,168,092 describes a probing instrument with a tubing which becomes extraverted under pressure, whereby the tubing exerts pressure on the walls of the cavity to separate the walls thereof.
Accordingly, it is most desirable to employ a catheter, or like instrument, which has a certain level of stiffness in order to facilitate placement of the catheter with relative ease within the vascular system of a patient. However, as pointed out above, after placement of the catheter well into the vasculature, the initial level of stiffness is undesirable since more pliability and flexibility may be required. It can be seen, then, that it is desirable to be able to vary the degree of stiffness of the catheter so as to have a relatively high degree of stiffness during placement of the catheter into the patient and then a relatively low degree of stiffness for final positioning.
A catheter having a variable flexibility, or flexural modulus, for insertion into a body comprises a length of flexible tubing having a normally relatively low flexural modulus. A lumen inside the tubing provides a free flow path therethrough. A fluid control system is associated with the tubing for controllably increasing the flexural modulus of the tubing to stiffen the same during insertion of the tubing into the body. After being positioned in the body, the fluid control system is adjusted to allow the tubing to return to its normally relatively low flexural modulus.
In the preferred embodiment of this aspect of the invention, the means for increasing the flexural modulus of the tubing includes a lumen associated with the catheter tubing. This lumen is coupled to one or more fluid cavities within the catheter tubing and to a pressure source. An increase in pressure in the lumen serves to increase the flexural modulus of the catheter tubing at one or more regions defined by the cavities with the pressure being controllable so that the flexural modulus of the catheter is also controllable. This lumen may be a second tube located within the catheter tubing.
In accordance with the principles of the present invention, the catheter advantageously offers the desirable stiffness characteristic during the placement or insertion stage into the body, while also providing the ability to reduce the stiffness after final positioning so that the catheter may be pliant and flexible for final positioning. Accordingly, the catheter, or like instrument, of the present invention allows the operator to manipulate the catheter into the patient with relative ease and substantially eliminates, or reduces, the awkwardness which accompanies the insertion of catheters which do not have the variable stiffness feature.
There is provided a catheter according to the invention for use within the vasculature of the human body comprising a flexible outer cylindrical tubing having an inner lumen and proximal and distal ends, a first cylindrical sealing plug positioned within the lumen of the cylindrical tubing at the distal end of the tubing, a second cylindrical sealing plug positioned within the lumen of the cylindrical tubing and spaced apart at a predetermined distance proximally from the first sealing plug so as to define a cavity between the first and second sealing plugs, a fluid passageway extending through the second sealing plug, and connector means connected to the proximal end of the catheter and having a lumen which is in fluid communication with the passageway of the second sealing plug so that fluid under pressure may be applied to the connector means to fill the cavity between the first and second sealing plugs to thereby stiffen the catheter in a region between the first and second sealing plugs.
Also, the catheter preferably includes a cylindrical spacer disposed between the first and second sealing plugs to maintain the predetermined distance between the sealing plugs.
Still further, the cylindrical spacer has a central axis which is coaxial with the central axis of the first and second sealing plugs and the outside diameter of the cylindrical spacer is less than the diameter of the inner lumen of the cylindrical tubing of the catheter.
In addition, preferably the passageway which extends through the second sealing plug is defined by the wall of a longitudinal slot which extends through the second sealing tube and an adjacent portion of the wall of the inner lumen of the cylindrical tubing of the catheter.
Still further, the catheter includes a guidewire lumen which extends through and is coaxial to the central axis of the first cylindrical sealing plug, the cylindrical spacer and the second cylindrical sealing plug to thereby provide a guidewire lumen which is coaxial with the flexible outer tubing of the catheter.
In addition, the catheter includes a flexible guidewire slidably received by the guidewire lumen.
Further, the catheter includes a third cylindrical sealing plug positioned within the lumen of the cylindrical tubing and spaced apart at a predetermined distance from the second cylindrical sealing plug so as to define a second cavity between the second and third sealing plugs, and a fluid passageway extending through the third sealing plug and being in communication with the lumen of the connector means so that fluid pressure may be applied to the connector means to fill the cavities between the first and second sealing plugs and between the second and third sealing plugs to thereby stiffen the regions between the respective sealing plugs.
There is provided a catheter according to the invention is such that the cavity is ring-shaped. In this case the cavity has been arranged so as to surround the guidewire lumen.
There is also provided a catheter according to this invention in which the guidewire lumen may be used for other purposes, such as conveying a fluid through the catheter or for receiving a glass fibre cable.
Still further there is provided a catheter according to this invention which the passageway may be used to fill the cavity with a fluid such as a contrast medium, air or another liquid which may later be removed from the cavity.
The fluids to be applied inside the cavities may for instance be a contrast medium, used with imaging techniques such as MRI or when using X-radiation, air or a resin curing under the influence of visible or UV-light.